1. Field of the Invention
The present invention relates to a magnetostriction control alloy sheet having a low thermal expansion and a manufacturing method for the same, and in particular relates to a magnetostriction control alloy sheet advantageous as a shadow mask used in a CRT (cathode-ray tube) and a method of manufacturing for the same.
The present Specification is based on a Japanese patent application (patent application 2000-222335), the content of which is incorporated as a part of the present specification by reference.
2. Description of Related Art
Generally, in order to manufacture a shadow mask used for example in the display for a PC (personal computer), first, an alloy sheet is perforated by a photoetching process, and a plurality of apertures are formed that allow passage of an electron beam. Next, the obtained flat mask is softened and annealed, and subsequently, the softened and annealed flat mask is pressed by press formation into a shape that conforms to the shape of the CRT. Finally, the upper surface is blackened.
Specifically, in the softening and annealing process, softening and annealing is carrying out having the object to be softened at about 750 to 1000xc2x0 C. followed by carrying out press formation. In the typical shadow mask, a distorsion of several percent is imparted by this press formation. Then, after press formation, a blackening process is carried out at about 500 to 700xc2x0 C. in an oxidizing atmosphere.
In this manner, the alloy sheet is formed into a shadow mask through the sequence of etching and softening, annealing, press formation, and blackening processes, and then mounted in a CRT.
As an alloy used for the material of the shadow mask, soft steel sheets such as low carbon rimmed steel, low carbon aluminum killed steel, or the like were once used, but because these materials have a high coefficient of thermal expansion, they exhibit a large amount of doming, which is to say that the doming characteristics deteriorate. Doming is a phenomenon in which the shadow mask is heated and thermal expansion occurs due to the radiation of the electron beam that does not pass through the apertures of the shadow mask. Consequently, the electron beam that passes through the apertures of the shadow mask does not land on the determined position on the phosphorescent surface. In order to prevent this doming phenomenon, conventionally an Fexe2x80x94Ni invar (Ni 36%, remainder Fe) has been used.
In recent years, both the definition and flattening of the displays have progressed, and thus the plane strength must be further increased.
The plane strength of the shadow mask mounted in the CRT is formulated by the plane buckling strength of the sheet. This plane buckling strength is proportional to the square of the sheet thickness and the value of the Young""s modulus (E). Therefore, generally in the case of the same sheet thickness, using a material having a high Young""s modulus can increase the plane strength.
This means that in a material for a shadow mask, conventionally, a low coefficient of thermal expansion is required, and at the same time, a high Young""s modulus is required in order to further improve the plane strength.
However, in shadow masks that use current invar material, the Young""s modulus is still insufficiently high, and this is a problem for the plane strength. Therefore, a material for a shadow mask is required that maintains the low thermal expansion properties of an invar material and at the same time has a high Young""s modulus in the state following the final blackening process.
In contrast, in the case of using a general Fexe2x80x94Ni alloy in the shadow mask, the electron beam is deflected by the stray magnetic fields present in the external environment of the color Braun tube, and thereby xe2x80x9ccolor deviationxe2x80x9d occurs due to the failure of the electron beam to land on the predetermined pixel, which is of concern in terms of image quality problems.
Furthermore, the increasingly high density of the graphic displays and the like in color displays is progressing, and together with this, there is a trend for the electron beam density to increase, and thus the average current is increasing. Thus, due to the current produced when the electron beam passes through the apertures in the shadow mask, xe2x80x9ccolor deviationxe2x80x9d that occurs due to the shadow mask itself becoming magnetized is also a problem in terms of the image quality.
Therefore, as a material for a shadow mask, in order to prevent the influence of magnetization due to the terrestrial magnetism and the electron beam, the advantageous magnetic properties of high permeability and low coercive force are also required.
In consideration of the problems described above, it is an object of the present invention to provide an advantageous magnetostriction control alloy sheet, a manufacturing method for the same, and a part for a color Braun tube such as a shadow mask that has a low coefficient of thermal expansion, superior magnetic properties, and at the same time has a high Young""s modulus even after a blackening process.
The magnetostriction control alloy sheet according to the present invention is an alloy plate used in a part for a color Braun tube such as a shadow mask, and is characterized in that the magnetostriction xcex after softening and annealing is between (xe2x88x9215xc3x9710xe2x88x926) and (25xc3x9710xe2x88x926).
The magnetostriction control alloy sheet according to the present invention preferably incorporates C at 0.01 wt. % or less, Ni at 30 to 36 wt. %, Co at 1 to 5.0 wt. %, and Cr at 0.1 to 2 wt. %, and also incorporates Si at 0.001 to 0.10 wt. % and/or Mn at 0.001 to 1.0 wt. %, the remainder comprising Fe and unavoidable impurities.
In addition, the parts for a color Braun tube such as the shadow mask according to the present invention are characterized in using the above-described magnetostriction control alloy sheet as a material. Moreover, in addition to use as a shadow mask, another example of a part in a color Braun tube for which the present invention can be used is an inner seal or the like.
A manufacturing method for the magnetostriction control alloy sheet according to the present invention is characterized that after the Nixe2x80x94Fexe2x80x94Co alloy that incorporates C at 0.01 wt. % or less, Ni at 30 to 36 wt. %, Co at 1 to 5.0 wt. %, and Cr at 0.1 to 2 wt. %, and also incorporates Si at 0.001 to 0.10 wt. % and/or Mn at 0.001 to 1.0 wt. %, the remainder comprising Fe and unavoidable impurities, undergoes final annealing, there is a temper rolling process having a reduction ratio of 10 to 40%.
In the present invention, the final annealing temperature is 800 to 1100xc2x0 C. and the reduction ratio by cold rolling before this final annealing can be 50% or greater.
Moreover, in the present invention, the permeability denotes the maximum permeability. Therefore, both xe2x80x9cpermeabilityxe2x80x9d and xe2x80x9cmagnetostrictionxe2x80x9d are absolute numbers.
In addition, the xe2x80x9csoftening and annealingxe2x80x9d in the present invention denote softening and annealing carried out between the etching and press formation processes during the process in which the shadow mask is manufactured from an alloy sheet.
According to the present invention, due to restricting appropriately the composition and magnetostriction of the Nixe2x80x94Fe alloy and the Nixe2x80x94Fexe2x80x94Co alloy, a magnetostriction control alloy sheet having a high Young""s modulus and permeability and a superior plane strength is obtained. In addition, by appropriately restricting the reduction ratio of the temper rolling carried out after the final annealing, the magnetostriction is (xe2x88x9215xc3x9710xe2x88x926) to (+25xc3x9710xe2x88x926), and superior magnetic properties for the shadow mask are obtained even after the softening and annealing, press formation, and blackening processes, and at the same time, a high Young""s modulus is maintained, and stable physical properties are exhibited.